The present invention relates to pressure transmitters that sense process pressures and display or transmit an output with a magnitude representative of the process pressure.
Pressure transmitters are often installed in harsh environments that can affect the accuracy of the transmitter output. Transmitter outputs are also often corrected for present environmental conditions by a controller embedded in the transmitter, using a process called compensation. Arrangements have also been proposed to store the amplitude and duration of overpressure peaks, temperature, humidity and vibration so that an alarm is triggered when the pressure transmitter is damaged so extensively that it is near the end of its useful life as shown for example in Japanese Kokoku 2,712,701 (kokai Hei 3[1991]-229124).
It is found, however, that pressure sensors in pressure transmitters are subject to physical changes as a result of past overpressures long before the end of the transmitter""s life. These physical changes are especially likely to occur with pressure sensors that include metal components that are strained repeatedly by the overpressure. These physical changes result in degradation of the accuracy of the transmitter output, however this degradation can go unnoticed, resulting in degraded performance of the process and increased cost. This degradation is not corrected by known compensation arrangements which only address present environmental conditions. This degradation is also not identified by end-of-life alarms because degradation can occur early in the useful life of the transmitter.
A transmitter is needed which can predict a present magnitude of transmitter output error due to past overpressures. With such predicted magnitude available, service personnel can evaluate the magnitude of the error and take timely action to recalibrate the pressure transmitter if the error is too high.
A prediction of a present magnitude of transmitter output error due to past overpressures is calculated in a controller in a pressure transmitter. The controller calculates a predicted present magnitude of transmitter output error as a function of a record, accumulated in memory, of excessive sensor output levels and predetermined data, stored in the memory, predicting magnitudes of transmitter output error as a function of cumulative excessive sensor output levels. The controller generates a prediction output that can be read by service personnel or a control system for scheduling recalibration of the pressure transmitter.
The pressure transmitter includes a pressure sensor, adapted to sense process pressure, that couples to the controller. The controller generates a pressure transmitter output representing the magnitude of the process pressure.
The prediction output alerts service personnel when the pressure transmitter output may have shifted too much due to past overpressures, and the service personnel can take steps to recalibrate the pressure transmitter output.